GENEVA, Sept 5 (Reuters) - The World Health Organisation (WHO) said on Friday blood-derived products and serum from survivors may be used to treat Ebola virus immediately and two vaccines could be available for health workers by year-end.

Existing supplies of all experimental medicines are limited and will not be sufficient for months to come, while the outlook for vaccine supplies looks "slightly better", the WHO said in a statement after two-day talks attended by nearly 200 experts.

But good clinical care, rigorous infection prevention and control measures, and the tracing of people who have been exposed remain crucial for ending an epidemic that has killed at least 2,097 in West Africa since March, the U.N. agency said.

"There is a real opportunity that blood-derived products can be used now. This can be very effective in terms of treating patients," WHO assistant director-general Marie-Paule Kieny told a news conference in Geneva.

"With the negative point that we have so many patients, one positive point is there are also many people now who are convalescent, who survived and are doing well, These people can provide blood, serum to treat," she told a news conference.

"What is available will be used in the field to treat real patients as soon as possible."

Studies suggest that blood transfusions from Ebola survivors might prevent or treat Ebola virus infection in others, but it is not known whether antibodies in the plasma of survivors are sufficient, according to the United Nations health agency.

Two "promising" Ebola vaccines have also been identified after showing promising results in animals, and safety results from human clinical trials may be available from November, paving the way for their use, Kieny said.

The two vaccines are made by GlaxoSmithKline Plc and NewLink Genetics, according to WHO documents.

"These must be prioritised in terms of clinical development," Kieny said.

Clinical trials of the GSK vaccine have begun in the United States, while trials for the NewLink vaccine will start by mid-September in Europe and Africa, she said.

Pending initial results on the vaccines' safety, expected in November, they will be given to health care workers in the field as a priority, with their informed consent, she said.

"If we have good safety data, if the results are positive, they will start to be used in health care workers in order to protect and also to evaluate if it protects them," Kieny said.

"We will have results of safety by November 2014 and after that these vaccines will start to be rolled out starting with health care workers and front line workers in the field."

ZMAPP DRUG "ENCOURAGING"

ZMapp, made by the U.S.-based Mapp Biopharmaceutical Inc., has been given to seven people infected with Ebola, including two American aid workers and a Briton who all recovered, but it remains unproven and supplies have run out. The U.S. government pledged up to $42.3 million this week to accelerate its testing.

"For the time being there's not enough experience to conclude whether this treatment works or not," Kieny said of the antibody drug ZMapp. "There seem to be encouraging signs."

"As soon as there are supplies available they will be tried."

Dr. Larry Zeitlin, president of the California-based Mapp Biopharmaceutical, told Reuters that Washington's support was vital to conducting early-stage safety studies of the drug as the jury is still out on both its safety and efficacy.

"The U.S. support will enable us to figure out what the appropriate dose is and scale up manufacturing. With a drug you have not only to make it, but make it consistently to the same quality. The award given us is for 18 months. We will probably be in human trials beginning in 2015," Zeitlin said in an interview on Friday on the sidelines of the WHO meeting.

"We don't have data indicating whether ZMapp is safe in humans, we don't have data that it works in humans. That is the whole point of performing clinical trials," he said. (Reporting by Stephanie Nebehay and Tom Miles; writing by Stephanie Nebehay; editing by Andrew Roche)